Differential gene expression analysis reveals pathways important in early post-traumatic osteoarthritis in an equine model.

BACKGROUND: Post-traumatic osteoarthritis (PTOA) is a common and significant problem in equine athletes. It is a disease of the entire joint, with the synovium thought to be a key player in disease onset and progression due to its role in inflammation. The development of effective tools for early diagnosis and treatment of PTOA remains an elusive goal. Altered gene expression represents the earliest discernable disease-related change, and can provide valuable information about disease pathogenesis and identify potential therapeutic targets. However, there is limited work examining global gene expression changes in early disease. In this study, we quantified gene expression changes in the synovium of osteoarthritis-affected joints using an equine metacarpophalangeal joint (MCPJ) chip model of early PTOA. Synovial samples were collected arthroscopically from the MCPJ of 11 adult horses before (preOA) and after (OA) surgical induction of osteoarthritis and from sham-operated joints. After sequencing synovial RNA, Salmon was used to quasi-map reads and quantify transcript abundances. Differential expression analysis with the limma-trend method used a fold-change cutoff of log2(1.1). Functional annotation was performed with PANTHER at FDR < 0.05. Pathway and network analyses were performed in Reactome and STRING, respectively. RESULTS: RNA was sequenced from 28 samples (6 preOA, 11 OA, 11 sham). "Sham" and "preOA" were not different and were grouped. Three hundred ninety-seven genes were upregulated and 365 downregulated in OA synovium compared to unaffected. Gene ontology (GO) terms related to extracellular matrix (ECM) organization, angiogenesis, and cell signaling were overrepresented. There were 17 enriched pathways, involved in ECM turnover, protein metabolism, and growth factor signaling. Network analysis revealed clusters of differentially expressed genes involved in ECM organization, endothelial regulation, and cellular metabolism. CONCLUSIONS: Enriched pathways and overrepresented GO terms reflected a state of high metabolic activity and tissue turnover in OA-affected tissue, suggesting that the synovium may retain the capacity to support healing and homeostasis in early disease. Limitations of this study include small sample size and capture of one point post-injury. Differentially expressed genes within key pathways may represent potential diagnostic markers or therapeutic targets for PTOA. Mechanistic validation of these findings is an important next step.

Histopathologic findings in the sacrocaudalis dorsalis medialis muscle of horses with vitamin E-responsive muscle atrophy and weakness.

OBJECTIVE: To characterize clinical findings, outcomes, muscle characteristics, and serum or muscle concentrations of α-tocopherol for horses with vitamin E-responsive signs of muscle atrophy and weakness consistent with signs of equine motor neuron disease (EMND). DESIGN: Retrospective case-control study. ANIMALS: 8 affected (case) adult horses with acute (n = 3) or chronic (5) gross muscle atrophy that improved with vitamin E treatment and 14 clinically normal (control) adult horses with adequate (within reference range; 8) or low (6) muscle concentrations of α-tocopherol. PROCEDURES: Medical records were reviewed, serum and muscle concentrations of α-tocopherol were measured, and frozen biopsy specimens of sacrocaudalis dorsalis medialis muscle and gluteal muscle were histologically evaluated for pathological changes. Fiber type composition and fiber diameters were assessed in gluteal muscle specimens. RESULTS: A myopathy that was histologically characterized by redistribution of mitochondrial enzyme stain (moth-eaten appearance) and anguloid atrophy of myofibers was evident in sacrocaudalis dorsalis medialis muscle fibers of the 8 affected horses that had low serum (6/8) or skeletal muscle (5/5) concentrations of α-tocopherol; these histopathologic changes were not found in muscle specimens of control horses with low or adequate muscle concentrations of α-tocopherol. All affected horses regained strength and muscle mass within 3 months after initiation of vitamin E treatment and dietary changes. CONCLUSIONS AND CLINICAL RELEVANCE: A vitamin E-deficient myopathy characterized histologically by a moth-eaten appearance in the mitochondria and anguloid myofiber atrophy in frozen sections of sacrocaudalis dorsalis medialis muscle biopsy specimens was found in horses with clinical signs of EMND that were highly responsive to vitamin E treatment. This myopathy may be a specific syndrome or possibly precede the development of neurogenic muscle fiber atrophy typical of EMND.